When a supplemental power source, such as a three-phase generator, is connected to a power grid, a small difference in the frequency, phase angle, or magnitude between the source and the grid can create very large over current. This is because the voltage source usually has very low impedance. The over current condition can trigger the power grid to "shut-down" or may damage circuit components.
Therefore, it is necessary when connecting a supplemental power source to a power grid to guarantee that the three phase output voltage of the power source has the same phase sequence, the same phase angle, and the same magnitude and frequency as the three phase voltage of the power grid. This is called synchronization of the power source and the power grid.
In the prior art, it is known to employ a phase lock loop technique to control the phase synchronization of the supplemental power source (SPS) and the power grid. Prior to the present application, this technology is basically a hard-wired configuration requiring hardware and associated hardware control technology. This technique requires separate phase and magnitude detecting circuits to control the voltage phase and magnitude of the supplemental power source. Extra circuitry is required to calculate the frequency of the supplemental power source or the power grid.